In many parts of the United States, rainfall is insufficient and/or too irregular to keep turf and landscaping green and therefore irrigation systems are installed. Such systems typically include a plurality of underground pipes connected to sprinklers and valves, the latter being controlled by an electronic irrigation controller. One of the most popular types of sprinklers is a pop-up rotor-type sprinkler. In this type of sprinkler a tubular riser is normally retracted into an outer cylindrical case by a coil spring. The case is buried in the ground and when pressurized water is fed to the sprinkler the riser extends. A turbine and a gear train reduction are mounted in the riser for rotating a nozzle turret at the top of the riser. The gear train reduction is often encased in its own housing and is often referred to as a gear box. A reversing mechanism is also normally mounted in the riser along with an arc adjustment mechanism.
The gear drive of a rotor-type sprinkler can include a series of staggered gears and shafts wherein a small gear on the top of the turbine shaft drives a large gear on the lower end of an adjacent second shaft. Another small gear on the top of the second shaft drives a large gear on the lower end of a third shaft, and so on. Alternatively, the gear drive can comprise a planetary arrangement in which a central shaft carries a sun gear that simultaneously drives several planetary gears on rotating circular partitions or stages that transmit reduced speed rotary motion to a succession of similar rotating stages. The planetary gears of the stages sometimes engage corresponding ring gears formed on the inner surface of the housing. See, for example, U.S. Pat. No. 5,662,545 granted to Zimmerman et al.
Two basic types of reversing mechanisms have been employed in commercial rotor-type sprinklers. In one design a reversing stator switches water jets that alternately drive the turbine from opposite sides to reverse the rotation of the turbine and the gear drive. See for example, U.S. Pat. No. 4,625,914 granted to Sexton et al. The reversing stator design typically employs a long metal shaft that can twist relative to components rigidly mounted on the shaft and undesirably change the reverse point. Stopping the rotation of the stator and changing direction of rotation via alternate water jets does not provide for repeatable arc shift points. Persons that manually set the arc of rotor-type sprinklers that employ a reversing stator design do not get a tactile feel for a stop at the set reverse points.
A more popular design for the reversing mechanism of a rotor-type sprinkler includes four pinion gears meshed together and mounted between arc-shaped upper and lower frames that rock back and forth with the aid of Omega-shaped over-center springs. One of the inner pinion gears is driven by the gear train reduction and the pinion gears on opposite ends of the frames alternately engage a bull gear assembly to rotate the nozzle back and forth between pre-set arc limits. The arc limits are effectuated by a shift dog alternately engaging a fixed arc tab and an adjustable arc tab. See for example, U.S. Pat. Nos. 3,107,056; 4,568,024; 4,624,412; 4,718,605; and 4,948,052, all granted to Edwin J. Hunter, the founder of Hunter Industries, Inc., the assignee of the subject application. The entire disclosures of the five patents just listed are hereby incorporated by reference. While the reversing frame design has been enormously successful, it is not without its own shortcomings. It involves a complicated assembly with many parts that can have operational failures. The main drawback of the reversing frame design is that the pinion gears are held in contact to the outer bull gear with a spring force that is relatively weak. Therefore high head torque forces which are sometimes experienced with this type of sprinkler can cause the reversing frame gears to slip out of engagement or wear out.
Adjusting the arc of coverage of a rotor-type sprinkler is a manual process performed by the user. Some commercially available rotor-type sprinklers are designed to have their arc adjusted from the top of the sprinkler. Typically the arc adjustment mechanism of these sprinklers has a gear reduction such that takes several turns of an arc adjustment shaft to cover the full range of arc setting adjustment. Other commercially available rotor-type sprinklers use an arc adjusting ring that is located on the side of the sprinkler riser that provides a one-to-one arc setting adjustment.